How should concrete carbonization be solved?

Concrete carbonization.

For the prevention and control of damage, we have summarized a series of treatment measures in the construction of concrete: First, the construction should be based on the geographical location of the building.

surrounding environment, choose the right cement type; For the water level change area and the parts of the alternating dry and wet action or the more severe cold areas, sulfate-resistant ordinary cement is selected.

High-strength cement should be selected for the scouring part; Second, the properties of aggregates are analyzed, such as the effect of acid-resistant aggregates with water and cement on the carbonization of concrete to a certain extent; Third, it is necessary to select a good mix ratio, appropriate amount of admixtures, high-quality raw materials, scientific mixing and transportation, timely maintenance and other strict technological means to reduce the amount of seepage and the erosion of other harmful substances to ensure the compactness of concrete; In addition, if the building is located in an area with a harsh environment, it is advisable to adopt an epoxy base liquid coating to protect the effect, and set a protective layer around the underground part of the building; Concrete is impregnated with various solvents, such as smeared with melted asphalt. Also, if the building once the concrete carbonization occurs, it is best to use epoxy material to repair, if the carbonization depth is larger, the loose part of the concrete can be chiseled, the harmful substances that enter can be washed, and the concrete joint surface is chiseled.

Fill with epoxy mortar or fine stone concrete, and finally use epoxy base liquid as a coating base for protection.

Carbonization of concrete is a type of chemical corrosion to which concrete is subjected. The process of CO2 gas in the air penetrating into the concrete, and the chemical reaction with its alkaline substances to form carbonate and water, so that the alkalinity of the concrete is reduced, which is called concrete carbonization, also known as neutralization. CO2 gas in the air penetrates into the concrete, and the chemical reaction with its alkaline substances generates carbonate and water, and the process of reducing the alkalinity of the concrete is called concrete carbonization, also known as neutralization, and its chemical reaction is:

ca(oh)2+co2=caco3+h2o。The cement generates a large amount of calcium hydroxide in the hydration process, so that the concrete void is filled with saturated calcium hydroxide solution, and its alkaline medium has a good protective effect on the steel bar, so that the surface of the steel bar generates insoluble Fe2O3 and Fe3O4, which is called passivation film. After carbonization, the alkalinity of the concrete is reduced, and when the carbonization exceeds the protective layer of the concrete, under the condition of the presence of water and air, the concrete will lose its protective effect on the steel bar, and the steel bar will begin to rust.

It can be seen that the carbonization of concrete generally does not directly cause the deterioration of its performance, for plain concrete, carbonization also has the effect of improving the durability of concrete, but for reinforced concrete, carbonization will reduce the alkalinity of concrete, and at the same time, increase the number of hydrogen ions in the concrete pore solution, thus weakening the protective effect of concrete on steel bars. There are many factors that affect the carbonization rate of concrete.

First of all, the cement varieties are more affected, because the calcium silicate and calcium aluminate salts contained in different cements are different; Secondly, the influence of concrete carbonization is mainly related to the concentration of CO2 in the surrounding medium and the humidity, under the conditions of dry and saturated water, the carbonization reaction is almost terminated, so this is a very important reason in addition to the influencing factors of cement varieties; Thirdly, when infiltrating the concrete through which the water passes, the dissolution rate of lime will also determine whether there are substances in the water that affect the solubility of Ca(OH)2, such as when the water contains Na2SO4 and a small amount of Mg2+, the solubility of lime will increase, such as the Mg(HCO3)2 containing Ca(HCO3)2 in the water is very beneficial to resist the dissolution erosion. Because they form a carbonized protective layer on the surface of the concrete; In addition, the permeability coefficient of concrete, water permeability, excessive vibration of concrete, water renewal rate near concrete, water flow velocity, structural size, water pressure and curing method are closely related to the carbonization of concrete.

The carbonization of concrete is affected by comprehensive factors such as environment (temperature, humidity, C02 content), cement dosage, water-cement ratio, admixture and admixture, cement variety, aggregate variety, construction technology, etc., it is difficult to completely control it. Slow down the occurrence of concrete carbonization. The concrete batching plant is appropriately mixed with admixtures, high-quality admixtures are used, the quality of raw materials is strictly controlled, the mixing ratio is strictly followed, the slump of the mixture is controlled, and the slump is reduced as much as possible under the condition of meeting the pumping requirements.

The construction unit should strengthen the quality awareness education of the concrete construction team, do not only map the progress, regardless of the quality, it is strictly forbidden to add water to the concrete, the vibration should be compact, and the maintenance method, maintenance time and demoulding time should be strictly implemented in accordance with the relevant national specifications.

Concrete carbonization refers to the process in which the alkaline substances in the concrete react with the acidic gases in the air to form carbonates and water.

Carbonization is a hazard to concrete, which not only affects the durability of concrete, but also reduces the degree of protection of concrete to steel bars. Due to the evaporation of the water generated by the carbonization of concrete, leaving fine voids, it will affect the durability of concrete.

Introduction

We all know that there are a large number of alkaline substances in concrete, and a large number of experiments have shown that when the alkaline pH value in concrete is, its alkaline medium has a good protective effect on the steel bar, so that the surface of the steel bar generates insoluble Fe2O3 and Fe3O4, which is called passivation film.

After carbonization, the alkalinity of the concrete is reduced, and when the carbonization exceeds the protective layer of the concrete, under the condition of the presence of water and air, the concrete will lose its protective effect on the steel bar, and the steel bar will be corroded. Therefore, when pouring concrete, we should reduce the water-cement ratio as much as possible, vibrate and compact, make its surface quality good, and slow down the carbonization rate of concrete.

The carbonization of concrete is the process of chemical reaction between calcium hydroxide in concrete and carbon dioxide and other acid gases permeated into concrete.

1. After the carbonization of concrete, its compressive strength increases, the ductility decreases, and it has obvious brittleness.

Second, the concrete carbonization improves the bearing capacity of the beam, but the yield deflection and ultimate deflection of the beam will become smaller, and the deformation capacity will be reduced.

3. Carbonization causes the concrete to carbonize and shrink, which will lead to fine cracks on the surface of the concrete.

You don't have to worry, we can choose concrete anti-carbonization coating during specific construction, which can effectively prevent the erosion of concrete by corrosive media such as carbon dioxide, chloride, oxygen and seawater acid rain in the environment.

Answer]: a, b, d

Page 30 of the 2020 textbook.

Carbonization reduces the alkalinity of concrete, weakens the protective effect of concrete on steel bars, and may lead to steel bar erosion; The carbonization of the Qingtong stool significantly increases the shrinkage of the concrete, increases the compressive strength of the concrete, but may produce microcracks before the banquet, and reduces the tensile strength and flexural strength of the concrete.